1. Field of the Invention
The present invention relates to a technology for controlling an illumination state by headlamps of a vehicle.
2. Description of the Related Art
When driving a vehicle at night, a driver checks ahead of the vehicle basically by illuminating a road by headlamp on low beams, and by, if necessary, illuminating the road by high beams. However, when light is radiated above what is commonly referred to as a cut-off line, this may cause a glare to oncoming vehicles and leading vehicles (hereinafter these will be referred to as “front vehicles”). Consequently, in recent years, various technologies have been proposed to prevent glare by detecting positions of front vehicles and controlling a radiation pattern of high beams not to radiate light in positions where front vehicles are present. For example, Japanese Unexamined Patent Application Publication No. 2010-232081 and Japanese Unexamined Patent Application Publication No. 2009-227088 disclose vehicle headlamps that produce shade to prevent glare against front vehicles by detecting the positions of the front vehicles, placing a mask with dimensions corresponding to the vehicles in a position corresponding to the vehicles ahead of a light source, and projecting light from the light source via this mask by means of a projector (image forming device). With these conventional examples, a shape of the mask is configured to be variable, and the part to be shaded is controlled on a variable basis according to the shape of that mask. Front vehicles are detected by performing an image recognition process using images captured by a camera mounted on a subject vehicle (see, for example, Japanese Unexamined Patent Application Publication No. 2009-298344). In this way, by controlling radiation pattern of high beams adequately, it is possible to prevent glare against front vehicles while radiating light in other areas, so that it is possible to contribute, for example, to find pedestrians early and to improve long-distance visibility.
Now, with the above-described conventional examples, normally, light from headlamps of oncoming vehicles and tail lamps of leading vehicles is extracted from image(s) captured by a camera, and positions of the vehicles are detected based on extracted light. Given this situation, for example, when a front vehicle approaches a curved road, or when a front vehicle changes a lane on a straight road, and a relative positional relationship between the front vehicle and the subject vehicle changes, it takes some time to detect the positional relationship after the change, generate a light distribution control signal, and change the radiation pattern of high beam based on the light distribution control signal. Such time lag may cause an inconvenience that high beam is temporarily caught in a side minor of the front vehicle and cause a glare to the front vehicle for a while.